Model Output Discussions 18z 31/01/2016

[karlos1983]

It's a tough one to call this. I wouldn't be at all surprised if the lows slide right under us and go into France leaving us wondering what all the fuss was about, how many times have we seen this sort of setup correct further and further south. 

Interesting times for model watching that's for sure. Nice to see the ECM join the party(ish) this morning. It's operational looks to be on the mild side later on, but that's after losing its way to go on the cold side at around the 14th.

 

[weirpig]

Again still a long way out  but snow for wales and england on gfs 6z  for  friday

[Nick F]

49 minutes ago, tight isobar said:

Well the slider LP could just become a coastal 'clipper' with a wintry mix on the coast's and weak northern most snow precipitation on its vwry leading edge. 

However @3-4 days out even as a gambling man...I wouldn't take the punt. As with sliding scenarios any incur/correction northwards could see dilution of air and some moderate/heavy snowfall over a large quadrant of land.far to early given the obvious miss-modeling @early range!..but at least both ample opportunity and something of interest in the winter of bore. ....thus far!

It appears the trend has been to track the lows sliding SE late week/Saturday further south over last few runs, so we could go south further with not much precip to show for apart from the SW. If the low on Saturday does track anything like the 00z EC and GFS show and the 06z is similar to the 00z, then the shallower the better in terms of snowfall. 00z GFS was deeper than ECM, the deeper the low the more mixing involved of less cold air. Ideally, as John H mentions above, we need to see light winds and heavy precip to create evaporative cooling to occur to allow snow to fall away from the favoured higher ground in the west - where coldest air will be moving down from the north on the back of the low.

There's fairly good model agreement on the broadscale picture into the medium range, the Euro longwave trough disrupts to allow high pressure to build in from the west and a cold northerly to start early next week, the high collapsing SE as trough and strong jet streak drops SE from Greenland/NE Canada with a return to westerlies.

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

However, yesterday's MJO forecasts were at odds, ECMWF had little amplitude in the MJO wave whereas GFS was gun-ho with a greater amplitude through to phase 7, so be interesting to see that today's MJO forecasts show. So the jury's out whether the MJO may have any effect on the wave paterns, because i it doesn't we could be back into default Atlantic dominated westerles to end the month.

Edited February 9, 2016 by Nick F

[I remember Atlantic 252]

1 minute ago, weirpig said:

Again still a long way out  but snow for wales and england on gfs 6z  for  friday

need hi res charts, only shows snow for hiils, esp Wales, low is slightly too far north 

[weirpig]

3 minutes ago, I remember Atlantic 252 said:

need hi res charts, only shows snow for hiils, esp Wales, low is slightly too far north e

But it goes to show the low isnt nailed yet  could be anywhere

[cheshire snow]

Just shows why Meto are so uncertain 

on Friday's LP,as the GFS06 sends the

snow line back north

C.S

[Polar Maritime]

The 6z shows the snow line further North over the Midlands next Friday before cold -8c 850's cover the Uk from the N/E.

Stronger Heights over Greenland also being sucked up by the Low.

Edited February 9, 2016 by Polar Maritime

[Nick F]

To avoid any confusion, there are 2 lows from GFS, one shallow one tracking across the south on Friday, snow on the northern flank of the precip (not to be taken literally) and another deeper low tracking on a more southerly track on Saturday which could bring snow further south as cold air undercuts from the north

Friday

Saturday

Friday's low most probably a damp squib for most IMO, away from high ground of Wales and N England. But Saturday could see a bigger threat of lowland snow as much colder air works further south on the back edge of the low clearing into the near continent. Subject to change this far off, but some white surprises at lower levels on Saturday not out the equation for now.

Edited February 9, 2016 by Nick F

[Frosty.]

The Gfs 6z shows potential wintry fun on Friday and into the weekend as Atlantic systems pushing in from the southwest bump into increasingly colder air becoming established across the UK with a risk of rain turning to sleet and then wet snow...so there could be some snowy surprises towards the end of this week!

[Polar Maritime]

Into the run and a wintry N/Wly flow takes hold from next Wednesday. Nothing mild on the cards with the Jet South of the UK.

Edited February 9, 2016 by Polar Maritime

[Man With Beard]

Surprise snowfalls? I'd be surprised if there weren't. Channel low. February 13th. Low passes through channel, low exits through the channel. No southerly input for the UK. For most mainland Britain, uppers dropping from -2C to -6C from easterly source (not westerly), and getting colder.

If we can't get snow out of these synoptics at this time of the year, I don't know just when we will.

[Snowynorth]

18 minutes ago, Nick F said:

To avoid any confusion, there are 2 lows from GFS, one shallow one tracking across the south on Friday, snow on the northern flank of the precip (not to be taken literally) and another deeper low tracking on a more southerly track on Saturday which could bring snow further south as cold air undercuts from the north

Friday

Saturday

Friday's low most probably a damp squib for most IMO, away from high ground of Wales and N England. But Saturday could see a bigger threat of lowland snow as much colder air works further south on the back edge of the low clearing into the near continent. Subject to change this far off, but some white surprises at lower levels on Saturday not out the equation for now.

Fridays low would bring more of a risk than Saturdays, it is actually the other way around. You have the colder air undercutting better further north but I suppose as its not the south it doesn't matter..

Edited February 9, 2016 by Snowynorth

[Frosty.]

1 minute ago, Man With Beard said:

 

 

If we can't get snow out of these synoptics at this time of the year, I don't know just when we will.

Agreed, it would be time to throw the damn towel..again if the synoptics shown between Friday and early next week don't produce some lying snow to some parts of the uk. It's a very interesting set up and there haven't been many this winter, this would be only the second cold snap in 10 weeks of winter across southern parts of the uk..Fingers crossed!

 

[terrier]

Looking at the gfs 06z certainly looks like the south could see some snowfall over the weekend with night frost. So certainly would feel raw over the snow fields. Seems like the ecm has also moved towards the gfs output this morning. So Midlands southwards I would say look best placed at the moment. We're as us further north look like remaining dry but I would settle for that after all this rain we have endured. 

[Frosty.]

7 minutes ago, terrier said:

We're as us further north look like remaining dry. 

There would be snow showers across exposed coastal parts of the north and east with a cold Ely / NEly flow.

[winterof79]

20 minutes ago, Karl. said:

There would be snow showers across exposed coastal parts of the north and east with a cold Ely / NEly flow.

Yes there would Karl.

And Derbyshire and Southern parts of Yorkshire are in the firing line if the 06z is to be believed

 

[nick sussex]

Well the ECM finally comes on board and now has a deeper cold pool to the ne. Hard to know why it has made such a mess of this set up but there are certainly red faces at ECM central and for the top ranking model this has been a dismal failure.

Anyway in typical NWP fashion the model that started out not interested switches and then has the better solution overall in terms of the medium term.

The sharpening up of that trough later on near the UK could bring something interesting and before then there does look sufficient cold to engage low pressure for some snow to fall.

Historically the models default set up here is to have things further north and then slowly edge south so we'll see if that's the case here.

The ECM isn't quite as amplified upstream at T120 and T144hrs as yesterday evenings run and this is a timeframe that might see a bit more amplitude which could have a knock on effect later with a better aligned ridge near Scandi. The T168 to T192hrs sees the possibilities of perhaps some trough disruption as the Azores high amplifies and edges nw.

Perhaps an MJO response here?

Overall then some chances for snow and a colder spell of weather likely, still a question mark however as to where any snow will fall as the track of these shortwave lows is very hard to predict accurately days ahead.

After this my interest is drawn to this sharpening up trend of the troughing near the UK, to see if that evolves further in future outputs.

 

[Frosty.]

Yes the Ecm 00z is now more in line with the other models and prolongs the cold next week compared to the 12z last evening, the cold lasts to the middle of next week across the southeast. I think some of us will see snow during this upcoming colder weather, either from showers or more organised frontal activity and there is no imby bias from me, I hope the south which has had almost diddly squat wintry weather so far, sees some lying snow!

[Polar Maritime]

Yes as others rightly put, It's nice to see the ECMWF on board after slogging behind over the last few days.. A cool/cold 'wintry' outlook across the models today for the next 10 days +

Edited February 9, 2016 by Polar Maritime

[Singularity]

Setting things up right for the weekend slider to deliver is largely about the balance between LP to the SE of the UK and that to the SW of the UK on Friday night. If the former is stronger, cold air moves south ahead of the latter and a cold undercut occurs. If the latter is stronger, there is more in the way of milder air thrown up ahead of it and most of the precipitation falls as rain. GFS (left-side) goes with that second outcome while ARPEGE (middle) has a kind of neutral situation which is hard to call going forward. ECM (right-side) is also pretty neutral but I think the slower arrival of the second slider is helpful in that there is more time for the colder air to feed south ahead of it - perhaps more of a rain to snow event for the south but a lucky few staying in the snow zone throughout.

  

Certainly the risk of the weekend slider ending up too far south anyway.

Should be the chance of snow showers on Monday if the flow can be more E than N. UKMO did this nicely on the 00z and the GFS 06z seems to have edged that way. That route also helps with the chance of seeing the Atlantic ridge topple 'onto' the low heights in Europe and find a foothold to the NE of the UK from which it can attempt to counter the attempts of the Atlantic trough to power through. Sometimes those rampant troughs end up as much less organised features... the adjustments for this weekend being a case in point.

[Mucka]

Quite naturally focus is on snow potential later this week but there are some subtle signals in FI that blocking may be possible later in the month.

I'm not sure how enthusiastic people will be for weak Easterly signal in FI, especially with more reliable cold and snow chances coming up but thought I'd mention for those hardy winter enthusiasts with a never say its over 'til its over attitude.

[Theresnoway]

Should people who are looking for the 6z GFS to verify, be concerned that the operational for London T850's was almost an outlier versus it ensemble suite for the coming weekend? Looking back at the 0z it was not much better, although joined by a couple of the ensembles.

There is definitely a trend towards colder, but the mean does not drop below -5, and that is not until Monday 15th February, well into la la land I would suggest.

Caution required, as ever.

[SxK]

31 minutes ago, Theresnoway said:

 

Should people who are looking for the 6z GFS to verify, be concerned that the operational for London T850's was almost an outlier versus it ensemble suite for the coming weekend? Looking back at the 0z it was not much better, although joined by a couple of the ensembles.

There is definitely a trend towards colder, but the mean does not drop below -5, and that is not until Monday 15th February, well into la la land I would suggest.

Caution required, as ever.

Generally best to stick to the operational and control runs when there is higher than normal uncertainty as they are run at higher resolution. 

Also an outlier by definition would place the operational run away from the other ensembles, that is not the case here although I agree it is at the bottom of the ensembles in terms of depth of cold for this weekend. 

But, yes, caution required as always is the case whenever cold is forecast, it is never straight forward for our little island. 

Edited February 9, 2016 by SxK

[snowray]

There simply isn't the depth of cold that we saw the other day digging well South over the whole of the UK, so when the PPN arrives it is only a wintry mess for the majority in Lowland England on the first slider. Wales/N Midlands above 100m look best, but only the very Northern boundary looks Wintry.

 

No point in discussing the 2nd low, could end up going into France, hoping for 12z upgrades on this one.

 

[mickpips]

26 minutes ago, snowray said:

There simply isn't the depth of cold that we saw the other day digging well South over the whole of the UK, so when the PPN arrives it is only a wintry mess for the majority in Lowland England on the first slider. Wales/N Midlands above 100m look best, but only the very Northern boundary looks Wintry.

 

No point in discussing the 2nd low, could end up going into France, hoping for 12z upgrades on this one.

 

So your taking ppn maps as gospel for the initial ( Friday low ) but discounting the secondary low ? as it 'may' end up in France. Very little movement of the initial low would mean that ppn forecast map to be incorrect too